Trisomy 7p resulting from isochromosome formation and whole‐arm translocation

Abstract

A newborn boy with a large anterior fontanel, minor facial anomalies, postaxial polydactyly, patent ductus arteriosus, and developmental delay had trisomy of 7p due to an i(7p) and a concomitant t(2;7) (q37.3;q11.1). Significant enlargement of the fontanel is the most characteristic finding in most patients with duplications involving 7p15-pter. Asynchrony in fore- and hindbrain and hemisphere formation leading to brain asymmetry and various defects in the posterior fossa are typical of infants with duplications of 7p11-p12. A variety of heart defects has also been found in more than 50% of patients with duplication of 7p segments. Isochromosome formation accompanied by whole-arm translocation, resulting in uniparental isodisomy for the involved segment, is an extremely rare cause leading to partial trisomies. Although it is not clear whether isochromosome formation precedes the whole-arm translocation or follows it, the secondary rearrangement may have adaptive significance.

A patient with isochromosome 18q, radial-thumb aplasia, thrombocytopenia, and an unbalanced 10;18 chromosome translocation

“…wiley.com. ] isochromosome formation has been centromere fission resulting in two telocentric segments, one of which (usually p arm) duplicates to form a stable isochromosome and the other segment translocates and fuses with a non-homologous telomere via telomere-centromere fusion [Lurie et al, 1995;Berend et al, 1999;Rivera et al, 1999].…”

Partial trisomy 7p defined by analysis of a complex chromosome rearrangement using a BAC clone panel

“…Our final interpretation of the CCR in the mother is as follows: ins(2;7)inv (7) Through the use of the BAC clone panel, the chromosome abnormality in our patient was conclusively identified as a partial trisomy of the short arm of chromosome 7 (7p12.237p21.3). Full or partial trisomy (duplication) 7p has been reported previously in 47 cases (for recent reviews see Cai et al, 1999;Pallotta et al, 1996;Reish et al, 1996;Lurie et al, 1995;Schaefer et al, 1995). 4 -8 Although the extent of the duplication varies among patients, a characteristic phenotype has emerged.…”

Partial Trisomy 2p and Partial Monosomy 2q Arising from a Paternal Intrachromosomal 2q-into-2p Between-Arm Insertion and Paracentric Inversion: Molecular Cytogenetic Characterization of a Four-Break Rearrangement

“…The majority of the cases reporting the trisomy 2p syndrome actually represent duplication-deletion syndromes, due to the inheritance of a derivative chromosome from a parent who carries a balanced translocation [Lurie et al, 1995]. The effect of these rearrangements on the clinical phenotype appears to correlate with the size of both the duplicated and deleted chromosomal segments [Bonaglia et al, 2000[Bonaglia et al, , 2009Giglio et al, 2000;De Brasi et al, 2001].…”

“…After reviewing the literature, several cases of partial duplication of chromosome 2 were identified encompassing segment 2p22.3p22.2 [Say et al, 1980;Parruti et al, 1989;Heathcote et al, 1991;Sawyer et al, 1994;Lurie et al, 1995;Mégarbané et al, 1997;Thangavelu et al, 2004;Kochilas et al, 2008]. Low-set ears, abnormal genitalia and congenital heart defect are probably some of the characteristics that our patient shares with 2p duplication syndrome.…”